This invention generally relates to the field of electrical systems that are employed to reduce the energy consumption of electrically-powered devices. More specifically, the present invention relates to an energy management device that employs a micro-controller and software system to regulate an A/C signal to reduce the energy consumption of an induction motor.
Reducing energy consumption is a prime goal in the world today. For consumers, reducing the amount of energy they consume individually lowers their personal energy costs. In addition, reduced energy consumption helps to conserve our natural resources and protect the environment.
At present, there are many energy saving systems in existence that reduce the energy consumption of electrical devices. One electrical device that can have its power consumption reduced by an energy saving device is an induction motor. Induction motors are commonly used for a wide variety of residential, commercial, and industrial purposes. The power requirements of an induction motor typically vary during operation. The inherent design of an induction motor causes it to use excessive current and voltage even under light or no load conditions. One measure of induction motor efficiency is to value the voltage applied as a function of motor load. Induction motors draw the same current whether loaded or unloaded. As a result, the motor efficiency decreases as the load decreases. In other words, an AC induction motor will consume much more energy than it requires under light load conditions.
AC induction motors are rather inefficient when they are not matched properly to their load. A motor is most efficient when it is heavily loaded and the rotor slips from its unloaded synchronous speed. As a bi-product of rotor slip, power factor is effected making the current closer in phase of the voltage.
Rotor slip can be induced not only by loading a motor, but also by reducing its average power supplied in such a manner as to remove sections of, the sinusoidal excitation waveform. Such a technique can greatly enhance the efficiency of the motor under light load conditions. The ultimate result is realized in power savings and lower operating costs.
Currently, many devices exist that vary the power supplied to the induction motor to enhance motor efficiency. U.S. Pat. No. 4,404,511 issued to Nola teaches a motor controller that is designed to enhance induction motor efficiency. A resistor is used to sense the input current to the motor. A circuit is used to generate a control signal that represents the phase shift difference between the motor current and motor voltage, which is the power factor. As the loading on the motor changes, the power factor changes. When the power factor is changed due to a decrease in the load on the motor, the device increases the off time of the duty cycle of the AC line power applied to the induction motor thereby reducing the current used by the motor. In this arrangement, the amount of power savings is scaled according to the power used by the device.
The key aspect of the device disclosed in Nola is that it senses the current using a resistive element. The Patent issued to Nola represents a class of energy management devices for induction motors that use resistive elements to measure current. The use of resistors to measure current has many disadvantages. First, the resistors required for measuring current are typically very large physically. This large physical size prevents the ability to fully miniaturize these devices. In addition, the cost of reliable resistive devices is typically very high. Further, resistors produce a great deal of heat while measuring the current. This heat reduces the efficiency of the device. Also, this heat can pose a design problem for the device since it also uses a microcontroller that must operate within a certain temperature range. It is therefore highly desirable to develop a system that can determine the phase shift without using a resistive element to measure current.
It is possible to determine a phase shift between the current and voltage without using a resistive element to measure the current. It is possible to determine the power factor by measuring the point where the current and voltage of and AC signal crosses zero. A voltage sampler circuit provides signals that indicate when the voltage applied to the motor crosses zero. An additional circuit is used to provide a signal that indicates when the current flow through the motor crosses zero. This system of measuring the power factor does not use any resistive elements. This method of sampling the zero point of the current and the voltage, referred to as the zero point system, has many advantages over the method that uses resistive elements. First, due to the fact that it uses no resistive elements, the zero point system is less expensive to manufacture. In addition, the zero point system uses less energy due to the lack of any resistors. Also, not using any resistors lowers the heat produced by the device. Finally, it is possible to miniaturize the circuitry of the zero point system to a greater extent since it does not include resistors.
U.S. Pat. No. 5,592,062 issued to Bach, the inventor of the technology disclosed in this application, teaches an energy controlling circuit for use with AC induction motors. The patent issued to Bach teaches the use of circuitry that determines when the current and voltage cross zero to find the power factor. This device utilizes a microcontroller in conjunction with a triac to control the duty cycle of the AC power applied to the motor. A voltage sensing circuit provides signals to the microcontroller. The micro controller is also coupled to the gate of the triac. The microcontroller automatically selects the appropriate parameters for most efficient motor operation based upon the motor power factor by the time at which the voltage across the motor crosses zero and the voltage at the triac gate crosses zero.
In addition to induction motors, various other electrical devices such as electric light bulbs do not operate at peak efficiency. It is also possible to enhance the electrical efficiency of these electrical devices by measuring the load across the light bulb and altering the input signal accordingly.
The present invention is an improved energy controller that increases the electrical efficiency of AC induction motors, electric lights, and other electrical devices. The invention is an integration of electrical circuitry and computer software to regulate the power supplied to the induction motor or electric light thereby enhancing the efficiency of the motor or light. As stated earlier, the inherent design of the induction motor causes it to use excessive current and voltage even under light or no-load conditions. The present invention takes advantage of this design by reducing the current and voltage consumed by the motor when not fully loaded. The frequency and peak voltage are not changed so the motor speed is not affected. The invention monitors the AC signal and senses when the motor is consuming more power than required. When the motor consumes more power than required, the invention removes a portion of the AC signal thereby allowing the motor to continue its rotational motion while consuming less energy. The amount of the signal that is removed, or xe2x80x9cclipped,xe2x80x9d is determined by the actual load on the motor. The actual load on the motor is calculated by the invention by comparing current and voltage phase angles. Under light loads, the amount of voltage removed from the AC signal is large. As the load demanded by the motor increases, the width of the slice removed from the signal will decrease, to the point where under fully loaded conditions the slice removed is negligible and full power is allowed to flow to the motor.
For electric lights, the microcontroller measures the loading across the light bulb and accordingly reduces the input A/C signal to the minimum level power level where the quality of light emitted from the light bulb is not reduced.
The present invention is comprised of a software-controlled microcontroller. The microcontroller is connected to circuitry that measures when the voltage and current cross the zero reference point along the current or voltage axis. In addition, the invention includes a bypass or relay circuit that can bypass the microcontroller and signal clipping circuitry and supply the input AC signal directly to the induction motor or electric light.
In addition, the present invention includes software that determines whether the device is functioning correctly. In the event the invention is not properly measuring the phase shift, or correctly clipping the AC signal; the software activates a bypass circuit and turns the remainder of the device off. The bypass circuit allows the AC input signal to flow unaffected to the induction motor or electric light. The use of this bypass circuit is also an improvement over patent, U.S. Pat. No. 5,592,062.
A further improvement over U.S. Pat. No. 5,592,062, is the use of a silicon control rectifier in place of the triac disclosed in the previous patent. The triac in the previous patent is used to control the amount of voltage supplied to the motor. The silicon control rectifier performs the same function. However, the silicon control rectifier has many advantages over the triac making the present invention superior to the invention disclosed in U.S. Pat. No. 5,592,062. The silicon control rectifier is cheaper to manufacture and is physically smaller in size.
In addition, the present invention is designed to provide a xe2x80x9csoft startxe2x80x9d for induction motors. Induction motors draw a large amount of power when they are turned on thereby placing a lot of strain on the power system supporting the motor. One way to eliminate the strain on the power system caused by turning on the induction motor is to soft start the motor. A soft start occurs when the voltage applied to the motor is gradually raised.
The primary object of the invention is to provide a new and improved energy control device for induction motors and electric lights.
It is another object of the invention is to provide circuitry and software that will shut the device down if it is not functioning correctly.
Another object of the invention is to use software to measure the power factor thereby eliminating the need for a resistive element to measure the current going through the motor or electric light.
A still further object of the invention is to pass the input AC signal directly to the induction motor or electric light in the event that the device is shut down.
Another object of the invention is to reduce the cost and size of energy control devices by replacing the triac circuit with a silicon control rectifier.
A further object of the invention is to provide an option to have a soft start for induction motors.
Further objects and advantages of the invention will become apparent as the following description proceeds and the features of novelty which characterize this invention are pointed out with particularity in the claims annexed to and forming a part of this specification.